Truck trailers used to transport perishable and frozen goods include a refrigerated trailer pulled behind a track cab unit. The refrigerated trailer, which houses the perishable or frozen cargo, requires a refrigeration unit for maintaining a desired temperature environment within the interior volume of the container. The refrigeration unit must have sufficient refrigeration capacity to maintain the product stored within the trailer at the desired temperature over a wide range of ambient air temperatures and load conditions. Refrigerated trailers of this type are used to transport a wide variety of products, ranging for example from freshly picked produce to frozen seafood.
One type of transport refrigeration system used in connection with truck trailers includes an electrically powered refrigeration unit operatively associated with the trailer. The refrigeration unit includes an engine driven electric generator, and the two are contained in a framework that is attached to the front wall of the trailer behind the truck cab. The refrigeration unit circulates air or another gas within the interior volume of the trailer to condition the cargo stored therein. The electric generator is driven by a diesel powered engine and is adapted to produce AC current at a selected voltage and frequency to power components of the refrigeration unit.
It is desirable that truck/trailer refrigeration units operate efficiently over a wide range of refrigeration capacity demands. Further, the refrigeration units must be capable of providing sufficient increased refrigeration capacity during pull-down (i.e., rapid cool down) to reduce the temperature within the cargo box of the trailer down to the desired storage temperature when perishable product is loaded. However, in some known systems, the generator consumes large amounts of fuel to produce power for the refrigeration unit, especially during pull-down. Accordingly, it is desirable to provide supplemental cooling to the refrigeration unit to reduce the fuel consumption and/or size of the generator.